Thanks for your answers!
To clarify a bit, I didn't mean a feature like 'export to... <dropdown list with every forum software imaginable>', rather some standard way of accessing and backing up the data. In case of blogs (let's take Ghost for example) there is information on where the DB (sqlite file) resides and an export option that results with (probably huge) json file. Having that, you can tinker a bit and come up with script transforming that json into whatever you might need.
Good point, though, is mention about Redis dump file. Probably would be good for me to read more about it (right now Redis is for me some enigmatic cloud of data residing in RAM mostly, though I do understand it has to be backed up periodically).